The compound of the formula (I) having a peripheral vasodilator effect is well known, its preparation and medicinal effect are disclosed in the British patent specification No. 2,174,701.
The racemic 1-ethyl-1-(acyloxymethyl)-1,2,3,4,6,7,12,12b.alpha.-octahydro-indolo[2,3-a ]quinolizine derivatives used as starting materials in the process described in the British patent specification No. 2,174,701 can be prepared by a method disclosed in the British patent specification No. 1,499,546 by reacting 1-ethyl-2,3,4,6,7,12-hexahydro-indolo[2,3-a]quinolizine of the formula (II) ##STR3## with formaldehyde used in a high excess. In this case the racemic form of the compound of the formula (I) is obtained. As disclosed in the British patent specification No. 2,174,701, the therapeutically effective .beta.-ethyl-derivative of the formula (I) can be prepared by acylating the above racemic compound, then by resolving the acylated compound thus obtained and then by deacylating the separated .beta.-ethyl form in four reaction steps. The yield of the pharmaceutically ineffective .alpha.-ethyl derivative separated in the resolution step is only about 25%, calculated for the starting hexahydro-indolo[2,3-a]quinolizine of the formula (II) when considering the yield data described in Examples 1 and 2 of the British patent specification No. 1,499,546 and Examples 1 and 2 of British patent specification No. 2,174,701.